1. Field of the Invention
The present invention relates to an apparatus for depositing thin films on a semiconductor wafer.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional thin film deposition apparatus comprises a reactor 1, first and second pipes 2 and 3 through which first and second reaction gases are injected into the reactor 1, and an exhaust pipe 4 for exhausting the reaction gases from the reactor 1. Also, first and second valves 5 and 6 which are opened or closed by a controller (not shown) are connected to the fist and second pipes 2 and 3, respectively, and a pump 7 is installed in the exhaust pipe 4.
In the apparatus with the above structure, the controller closes the second valve 6 and opens the first valve 5, the first reaction gas is provided through the first valve 5 to the reactor 1, and then exhausted through the exhaust pipe 4 and the pump 7. Then, the controller closes the first valve 5 and opens the second valve 6, the second reaction gas is provided through the second valve 6 to the reactor 1, and then exhausted through the exhaust pipe 4 and the pump 7.
However, during a thin film deposition step, the reaction gases provided to the reactor are deposited over the entire inner wall of the reactor exposed to the reaction gases in addition to the wafer. Thus, a cleaning step for cleaning the inner wall of the reactor must be performed periodically.
Also, because the exhaust pipe 4 is installed at only one side of the reactor 1, the distribution of the reaction gases in the reactor 1, that is, between a part near the exhaust pipe 4 and another part far away from the exhaust pipe 4, is different. Such difference in distribution of the reaction gases in the reactor causes uneven distribution of the reaction gases on the wafer, thereby interfering with the laminar flow of the reaction gases over the wafer.